The role of unsuspected maternal infection in the pathogenesis of perinatal morbidity has assumed increasing importance as newer knowledge has accumulated. Classically, symptomatic infections have always been recognized as being responsible for much perinatal morbidity. Studies of asymptomatic bacteriuria have demonstrated a relation between unsuspected infection and perinatal morbidity. Recent observations in this laboratory now indicate a relation between genital mycoplasmas and such morbidity. It is proposed to explore further this relation by the the following approaches: 1) to continue ongoing studies of the effect of antimicrobial agents on the outcome of pregnancy, in terms of low birth weight, postpartum fever and associated morbidity; 2) to examine further the relation between changes in antibody titer to genital mycoplasmas and the outcome of pregnancy, with particular emphasis on the role of Ureaplasma urealyticum; 3) to study further the role of bacteremia due to genital mycoplasmas, and particularly that due to M. hominis, occurring during the second stage of labor; 4) To determine whether any specific serotype of M. hominis or of U. urealyticum is associated with morbidity; 5) to determine if genital mycoplasmas play a similar role in pregnancies of women from more affluent social classes that they do in those of the social classes that have thus far been studied; 6) to determine interactive affect between genital mycoplasmas and other microflora of the genital tract, including Chlamydia trachomatis, trichomonas, group B Streptococcus, Haemophilus vaginale, Herpes hominis, selected anaerobes, and related microflora; 7) to investigate further the possible effect of U. urealyticum as a suppressant to antibody formation; 8) to continue analyses of the antigenic components of the membrane of different strains of genital mycoplasmas, in order to develop better serologic tests, and in order to isolate in purified form the major antigenic components.